The present invention relates to carrier tapes and in particular to a reuseable carrier tape for transporting electronic components, pharmaceuticals, and the like during production and assembly operations.
In the assembly of various types of electronic devices, such as, for example, computers and related products, it is common to transport miniature and subminiature components from the component manufacturer to a customer's assembly station(s) by means of a carrier tape. At this point automatic equipment functions to remove the components from the carrier tape and mount the components to a circuit board or the like as may be required. The carrier tape (or transfer tape as it is sometimes referred to) may also function to bring different components to an assembly station in proper order for sequential assembly. Such tapes are often formed from an elongated base strip of plastic, foil or paper and are usually covered by a cover strip. The base strip is often provided with cavities which are sized to hold the components in a particular orientation. The cover strip is usually held in place by an adhesive or heat bond which must be peeled away at the assembly station to permit the component to be removed after the cover is stripped back. Typical examples of prior art carrier tapes are disclosed in U.S. Pat. Nos. 3,465,874; 3,650,430; 3,700,019; 3,894,896; 3,910,410 and 4,298,120.
A problem often associated with such prior carrier tapes is that the top tape or cover sheet must be securely affixed to the bottom tape or base and the adhesive bond must subsequently be broken without damaging the carrier tape or sticking to the component since this could interfere with the transport and assembly mechanism. An essential requirement of the top tape is that it must separate from the bottom carrier tape at a known and predictable rate without disturbing the components. This is known as consistent peel strength. In the past adhesives and heat sealing were the principal means for sealing the top and bottom tapes which often rendered these non-reuseable. In many ultra-clean applications the use of such adhesives and heat bonds is undesirable out of concern that residue may contaminate the component or mounting board. In addition, heat seal bonds are generally non-uniform due to the occurrence of tiny hills and valleys on the strip during the heating operation. This may result in the cover sheet stripping away prematurely, (which could result in lost components) or remaining in place overly long. In either event the automatic operation would be interfered with.
Also, with many electronic components it is desirable to load the carrier tape with static-dissipative or conductive materials to prevent or dissipate any build-up of electrostatic charge. These materials often tend to interfere with the bonding characteristics of the adhesives used.
In U.S. Pat. Nos. 3,465,874 and 3,650,430 an attempt is made to solve these prob1ems by providing spaced snaps or push buttons on one of the strips to engage spaced holes in the other of the strips. This arrangement, obviously requires somewhat precise alignment of the snaps and openings in order to operate. Further, the strips are not uniformly secured to each other but rather continuously oscillate between secured and non-secured conditions.
In copending application Ser. No. 913,131 an improved carrier tape construction is described in which the base and cover strips are uniformly and consistently secured to each other and which requires a uniform force for separation so that they may readily be separated in a precise manner. At least one of the strips is provided with an integrally formed, longitudinally extending continuous profile which cooperates with surfaces of the other strip to secure the two in a locking engagement. While this arrangement solves most of the problems associated with prior art carrier tapes it requires relatively complex, and hence, relatively expensive extrusion techniques since the profile is formed integrally with at least one of the base and cover strips. This also limits, to some extent the configuration of and location of the profile. In addition, the carrier tape must be configured for a particular component to be transported as well as a particular drive arrangement since the former determines the cavity configuration and spacing while the latter determines the sprocket hole sizing and spacing.
In view of the above, it is the principal object of the present invention to provide an improved carrier tape construction which incorporates the advantages of the carrier tape disclosed in application Ser. No. 913,131 but which more readily lends itself to more conventional and economic manufacturing techniques.
A further object is to provide such a carrier tape wherein there is a greater degree of flexibility with regard to the associated components and drive assemblies than has heretofore been available.